The Mass Spectrometry (MS) Shared Resource provides mass spectrometry services and consultation to Cancer Center members at the University of Utah. This powerful tool is utilized in a range of investigations involving molecular characterization, such as identification of proteins from 1D or 2D gels at fmol to low pmol levels, peptide and oligonucleotide sequencing, and structure elucidation of new potential anti-tumor agents. Molecular mass measurements are highly accurate, with typical errors of 0.25Da at Mr 1,000, or 2Da at 30kDa. Data are acquired using electrospray ionization LC/MS/MS techniques, or by matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometry. Interpretation of MS data, planning of experiments, and discussion with laboratory members are provided as appropriate by the Resource Manager or Director, thus providing expertise not available in some biologically-oriented laboratories. Services were provided to cancer center members (with peer-reviewed funding) in 21 laboratories in 2002. Fee-for-service billings are handled electronically on a monthly basis as part of the central core facility billing system. A three-person advisory committee of individuals with relevant expertise provides advice on day-to-day operational problems as well as the development and future direction of the resource.